Abstract: Using the sandwich enzyme-linked immunosorbent assay (ELISA) for grass carp (Ctenopharyngodon idellas) growth hormone and different administrations of rcGH,we investigated the possibility of rcGH absorption by gastrointestinal tract of walking catfish (Clarias batrachus),northern sheatfish (Silurus soldatovi) and crucian carp (Carassius auratus gibelio).The specific ELISA can recognize endogenous GH in grass carp,jian carp and crucian carp blood and exogenous rcGH in northern sheatfish and walking catfish blood,but not endogenous GH in northern sheatfish and walking catfish blood.Rectal administration of rcGH to walking catfish (1 μg/g b.w.) and northern sheatfish (5 μg/g b.w.) resulted in rapid and marked increase in serum GH levels,suggesting that rcGH be absorbed by the intestine into the blood.In contrast,exogenous rcGH in serum was undeteted over a period of 48 h after an intragastic administration of rcGH (25 μg/g b.w.) to walking catfish.After an anterior intestine administration of rcGH (5 μg/g) to crucian carp,serum GH levels were significantly higher than the controls (P<0.001 or P<0.05) over a period of 33 h post administration.